1. Field
The present disclosure relates to a method and a system for controlling a tone reproduction curve (TRC) of an image printing system.
2. Description of Related Art
In today's business and scientific world, color has become essential as a component of communication. Color facilitates the sharing of knowledge and ideas. Companies involved in the development of digital color print engines are continuously looking for ways to improve the total image quality of their products. One of the elements that affects image quality is the ability to consistently produce the same quality image output on an imaging device or printer from one day to another, from one week to the next, month after month. Colors on a printer tend to drift over time due to ink/toner variations, temperature fluctuations, type of media used, environment, etc. There has been a long felt commercial need for efficiently maintaining print color predictability, particularly as electronic marketing has placed more importance on the accurate representation of merchandise in illustrative print or display media.
Color printing characterization is a crucial task in color management. The characterization process essentially establishes a relationship between device dependent, e.g., printer CMY, and device independent, e.g., CIELAB values. Several color management tasks such as derivation of ICC profiles, color transforms for calibration, etc. benefit from an accurate mathematical characterization of the physical device.
The most popular technique to build a printer characterization transform involves printing and measuring a large set of color samples, i.e., CMY(K) patches, in conjunction with mathematical fitting and interpolation to derive CMY(K) to Lab mappings. The accuracy of the characterization transform clearly depends on the number (N) of patches printed and measured. One aspect of patch measurement comprises a closed-loop uniformity correction system that generates multiple full-width patches of a single density across the whole printer page or photoreceptor belt (i.e., the entire cross-process position of the image printing system). Such full-width patches are measured by a full-width array sensor during cycle up to obtain a printer model of the tone reproduction curve (TRC) at each inboard to outboard pixel column. The measurement can then show the amount of toner or print ink printed at each position on that page by the particular halftone screen then used. Any variations in the TRCs (i.e. variations from the true intended color) are compensated for in the image path via remapping of the halftone TRC. Such remapping is generally referred to as spatially varying TRC corrections (SVT) and these remappings are unique for each color and each halftone screen. Also, in a conventional process control patch implementation, control patches for each developer housing are created in an inter-document zone (IDZ) between successive images on a drum or belt type photoreceptor that moves along a process direction. These control patches are sensed with toner patch sensors and actuators are adjusted to maintain a three-point toner response curve (TRC).
In the image printing system (that is using the closed-loop uniformity correction system), the absolute color is generally controlled in response to measurements of the three point TRC at the reference location using Vmag (development roll voltage), laser power, and Vmc (voltage difference between the development roll and the charged area of an image transfer surface) as actuators and color calibration is accomplished via a TRC halftone dot linearization routine. Because the reference location color (TRC) is controlled and calibrated through other means, there is no need for the closed-loop uniformity correction system to change the TRC at this reference location. Also, the closed-loop uniformity correction system corrects the TRC at all pixels to match the reference TRC while leaving the reference location unchanged (on average)
The present disclosure provides improvements in methods and systems for controlling a tone reproduction curve (TRC) of an image printing system.